The present invention is in the field of roofing and more particularly relates to a method of ballasting roof covering layers on substantially flat roof bodies. The purpose of ballasting roof covering layers on substantially flat roofs is to secure the required wind-steadiness of such roofs or, in other words, to prevent the roof covering layers on such roofs from being lifted from the basic roof bodies in stormy weather.
Up to now ballasting of the roof covering layers on flat roof surfaces is effected by applying thereon a layer of ballasting material in the form of gravel or (concrete) tiles.
Applying gravel has the disadvantage that in stormy weather the gravel may be caused to xe2x80x9crollxe2x80x9d, which may lead to a dangerous situation when gravel particles get off the roof. Moreover, working with gravel is rather labour-intensive, whilst the cleaning of a ballast layer composed of gravel constitutes an expensive factor in roof maintenance. Furthermore, gravel has become a scarce raw material.
The disadvantages mentioned hereinabove are particularly overcome by using concrete tiles (slabs) as a ballasting material. Concrete tiles, however, are relatively expensive and result in a relatively heavy roof load.
A primary object of the present invention is to provide an improved method of ballasting the roof covering layer(s) on a substantially flat roof body.
According to the present invention a mortar is applied to function as a ballasting material, said mortar being mainly composed of a mineral wool, a hydraulic binder and water.
In a composition of e.g. three parts of granulated mineral wool, one part of binder and one part of water such a mortar can be readily pumped and poured out over the roof covering layer(s) to be ballasted. Upon being poured out and straightened out the mortar sets and forms a slab with a porous or spongy structure, which has excellent drain quality and prevents puddle forming. The ballast layer obtained can be readily treaded as early as twenty four hours after pouring.
A ballast slab obtained by applying the method of the present invention results in a substantially reduction (viz. more than 50%) of the roof load as compared with a roof that is ballasted with concrete tiles of a comparable thickness (e.g. 5-7 cm).
In practice the mineral wool required is available in large amounts in the form of rockwool, that has been used in the substrate growing technique in horticulture.
Accordingly, with the method of the present invention advantageously and preferably use is made of granulated rockwool waste from the horticulture. In that case the method of the present invention not only results in a substantial improvement as compared with the well-known ballasting methods, but also provides a solution for the environmental problem connected with the production of rockwool waste.
The mineral wool mass may partly consist of glass fibre wool, large amounts of which become also available in the form of waste.
A practical mode of the method of the present invention is characterized in that joint strips or joint profiles are placed on the roof surface to be ballasted so as to divide the roof surface into panels, which are subsequently filled with mortar. In this way individual ballast panels or slabs (with a superficial area of e.g. 2-5 m2 may be obtained, which are separated from one another through joints. This avoids the forming of cracks and crevices in the ballast mass.
The joint strips or joint profiles respectively may also be used to function as a support guide for a smoothing instrument, which makes it easy to obtain a uniform ballast layer.
The joint strips may be of a permanent nature, if desired and may be in the form of a gutter profile to further improve the discharge of rain water.
Hereinabove mention has been made of the excellent drain quality and the inherent water water exorbing capacity of the ballast layer obtained with the method of the present invention. In order to achieve a quick discharge of the rain water collected in the ballast layer and thereby achieve a quick drying of the ballast layer, the roof surface to be ballasted may, according to a further feature of the invention, be providedxe2x80x94in advancexe2x80x94with an intermediate layer of a coarse open cellular structure. To realize such an intermediate layer use can e.g. be made of the kind of auxiliary material that is used in the horticulture in the initial germination phase of e.g. young tomato plants, which material is produced by shaping plastic sheet material through vacuum moulding into a plurality of closely adjoining, conically shaped miniature plant pots. Such an intermediate layer, that may have a thickness (height) of 1-2 cm, effects an immediate transfer of the rain water from the proper ballast layer towards the rain water outlet of the roof.
Artificial grass, in fact a perforate sheet of plastic with stud-shaped poles projecting from one side thereof, could be used instead. Such an intermediate layer of artificial grass could be applied with the poles directed to the roof surface to be ballasted.
Further features of the invention will be hereinafter further explained by way of example with reference to the accompanying drawing.